A method and apparatus for controlling a diesel fuel internal combustion engine with a solenoid-valve-controlled fuel-metering system are known from German Patent Application No. 40 04 110, which is not prior art with respect to the present application. The fuel-metering system comprises a fuel pump with a pump piston driven by the cam shaft. The piston pressurizes the fuel and feeds it into the individual cylinders. The feed start and the feed end can be determined by way of at least one solenoid valve. For this purpose, a control device calculates the control times for the solenoid valve, as a function of markings located on a shaft.
In such systems, however, the control device transmits control signals in the form of time variables. The precise start of injection must take place at a certain position of the crank shaft (angle variable). The end of injection occurs when the cam shaft has rotated a certain angle after the start of injection. For this reason, time variables have to be converted into angle variables, and angle variables into time variables, when using an rpm value. The accuracy of this conversion is largely dependent on the rpm value that is used.
Furthermore, German Patent Application No. 40 04 107, which is also not prior art with respect to the present application, describes a method and apparatus for controlling a solenoid-valve-controlled fuel pump. An electronic control apparatus calculates the starting and stopping times for one or more solenoid valves based upon the desired start of injection and the desired injection period. In this calculation, the switching times of the solenoid valves are taken into consideration.
In the calculation of the stopping time, the actual start of feed is included. In this apparatus, the end of feed is determined based upon the desired feed duration and the actual start of feed. In this apparatus, time variables are also processed. Since the injected fuel amount is significantly dependent upon the angle position of the cam shaft at the actual start of injection, i.e., at the actual feed start, when other conditions are constant, this method of operation results in a significant error in the quantity of fuel injected into the engine.
It is an object of the present invention to improve the accuracy of fuel metering in a method and apparatus for controlling of a solenoid-valve-controlled fuel-metering system.